From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751663AbdJ3HRQ (ORCPT ); Mon, 30 Oct 2017 03:17:16 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:52362 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751423AbdJ3HRJ (ORCPT ); Mon, 30 Oct 2017 03:17:09 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org C435B6028B Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=prsood@codeaurora.org From: Prateek Sood To: longman@redhat.com, peterz@infradead.org, tj@kernel.org, lizefan@huawei.com, mingo@kernel.org, boqun.feng@gmail.com, tglx@linutronix.de Cc: Prateek Sood , cgroups@vger.kernel.org, sramana@codeaurora.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] cgroup/cpuset: remove circular dependency deadlock Date: Mon, 30 Oct 2017 12:46:45 +0530 Message-Id: <1509347805-23491-1-git-send-email-prsood@codeaurora.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <45cdac2f-4462-e5b5-d724-8cca58e3932a@codeaurora.org> References: <45cdac2f-4462-e5b5-d724-8cca58e3932a@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Remove circular dependency deadlock in a scenario where hotplug of CPU is being done while there is updation in cgroup and cpuset triggered from userspace. Process A => kthreadd => Process B => Process C => Process A Process A cpu_subsys_offline(); cpu_down(); _cpu_down(); percpu_down_write(&cpu_hotplug_lock); //held cpuhp_invoke_callback(); workqueue_offline_cpu(); queue_work_on(); // unbind_work on system_highpri_wq __queue_work(); insert_work(); wake_up_worker(); flush_work(); wait_for_completion(); worker_thread(); manage_workers(); create_worker(); kthread_create_on_node(); wake_up_process(kthreadd_task); kthreadd kthreadd(); kernel_thread(); do_fork(); copy_process(); percpu_down_read(&cgroup_threadgroup_rwsem); __rwsem_down_read_failed_common(); //waiting Process B kernfs_fop_write(); cgroup_file_write(); cgroup_procs_write(); percpu_down_write(&cgroup_threadgroup_rwsem); //held cgroup_attach_task(); cgroup_migrate(); cgroup_migrate_execute(); cpuset_can_attach(); mutex_lock(&cpuset_mutex); //waiting Process C kernfs_fop_write(); cgroup_file_write(); cpuset_write_resmask(); mutex_lock(&cpuset_mutex); //held update_cpumask(); update_cpumasks_hier(); rebuild_sched_domains_locked(); get_online_cpus(); percpu_down_read(&cpu_hotplug_lock); //waiting Eliminating deadlock by reversing the locking order for cpuset_mutex and cpu_hotplug_lock. After inverting the locking sequence of cpu_hotplug_lock and cpuset_mutex, cpuset_hotplug_workfn() related functionality can be done synchronously from the context doing cpu hotplug. For memory hotplug it still gets queued as a work item. Signed-off-by: Prateek Sood --- include/linux/cpuset.h | 6 ---- kernel/cgroup/cpuset.c | 94 +++++++++++++++++++++++++++----------------------- kernel/power/process.c | 2 -- kernel/sched/core.c | 1 - 4 files changed, 50 insertions(+), 53 deletions(-) diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index a1e6a33..e74655d 100644 --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -51,9 +51,7 @@ static inline void cpuset_dec(void) extern int cpuset_init(void); extern void cpuset_init_smp(void); -extern void cpuset_force_rebuild(void); extern void cpuset_update_active_cpus(void); -extern void cpuset_wait_for_hotplug(void); extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask); extern void cpuset_cpus_allowed_fallback(struct task_struct *p); extern nodemask_t cpuset_mems_allowed(struct task_struct *p); @@ -166,15 +164,11 @@ static inline void set_mems_allowed(nodemask_t nodemask) static inline int cpuset_init(void) { return 0; } static inline void cpuset_init_smp(void) {} -static inline void cpuset_force_rebuild(void) { } - static inline void cpuset_update_active_cpus(void) { partition_sched_domains(1, NULL, NULL); } -static inline void cpuset_wait_for_hotplug(void) { } - static inline void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask) { diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 4657e29..ec44aaa 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -817,6 +817,18 @@ static int generate_sched_domains(cpumask_var_t **domains, return ndoms; } +static void cpuset_sched_change_begin(void) +{ + cpus_read_lock(); + mutex_lock(&cpuset_mutex); +} + +static void cpuset_sched_change_end(void) +{ + mutex_unlock(&cpuset_mutex); + cpus_read_unlock(); +} + /* * Rebuild scheduler domains. * @@ -826,16 +838,14 @@ static int generate_sched_domains(cpumask_var_t **domains, * 'cpus' is removed, then call this routine to rebuild the * scheduler's dynamic sched domains. * - * Call with cpuset_mutex held. Takes get_online_cpus(). */ -static void rebuild_sched_domains_locked(void) +static void rebuild_sched_domains_cpuslocked(void) { struct sched_domain_attr *attr; cpumask_var_t *doms; int ndoms; lockdep_assert_held(&cpuset_mutex); - get_online_cpus(); /* * We have raced with CPU hotplug. Don't do anything to avoid @@ -843,27 +853,25 @@ static void rebuild_sched_domains_locked(void) * Anyways, hotplug work item will rebuild sched domains. */ if (!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask)) - goto out; + return; /* Generate domain masks and attrs */ ndoms = generate_sched_domains(&doms, &attr); /* Have scheduler rebuild the domains */ partition_sched_domains(ndoms, doms, attr); -out: - put_online_cpus(); } #else /* !CONFIG_SMP */ -static void rebuild_sched_domains_locked(void) +static void rebuild_sched_domains_cpuslocked(void) { } #endif /* CONFIG_SMP */ void rebuild_sched_domains(void) { - mutex_lock(&cpuset_mutex); - rebuild_sched_domains_locked(); - mutex_unlock(&cpuset_mutex); + cpuset_sched_change_begin(); + rebuild_sched_domains_cpuslocked(); + cpuset_sched_change_end(); } /** @@ -949,7 +957,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus) rcu_read_unlock(); if (need_rebuild_sched_domains) - rebuild_sched_domains_locked(); + rebuild_sched_domains_cpuslocked(); } /** @@ -1281,7 +1289,7 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val) cs->relax_domain_level = val; if (!cpumask_empty(cs->cpus_allowed) && is_sched_load_balance(cs)) - rebuild_sched_domains_locked(); + rebuild_sched_domains_cpuslocked(); } return 0; @@ -1314,7 +1322,6 @@ static void update_tasks_flags(struct cpuset *cs) * * Call with cpuset_mutex held. */ - static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, int turning_on) { @@ -1347,7 +1354,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, spin_unlock_irq(&callback_lock); if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed) - rebuild_sched_domains_locked(); + rebuild_sched_domains_cpuslocked(); if (spread_flag_changed) update_tasks_flags(cs); @@ -1615,7 +1622,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, cpuset_filetype_t type = cft->private; int retval = 0; - mutex_lock(&cpuset_mutex); + cpuset_sched_change_begin(); if (!is_cpuset_online(cs)) { retval = -ENODEV; goto out_unlock; @@ -1651,7 +1658,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, break; } out_unlock: - mutex_unlock(&cpuset_mutex); + cpuset_sched_change_end(); return retval; } @@ -1662,7 +1669,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, cpuset_filetype_t type = cft->private; int retval = -ENODEV; - mutex_lock(&cpuset_mutex); + cpuset_sched_change_begin(); if (!is_cpuset_online(cs)) goto out_unlock; @@ -1675,7 +1682,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, break; } out_unlock: - mutex_unlock(&cpuset_mutex); + cpuset_sched_change_end(); return retval; } @@ -1714,7 +1721,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, kernfs_break_active_protection(of->kn); flush_work(&cpuset_hotplug_work); - mutex_lock(&cpuset_mutex); + cpuset_sched_change_begin(); if (!is_cpuset_online(cs)) goto out_unlock; @@ -1738,7 +1745,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, free_trial_cpuset(trialcs); out_unlock: - mutex_unlock(&cpuset_mutex); + cpuset_sched_change_end(); kernfs_unbreak_active_protection(of->kn); css_put(&cs->css); flush_workqueue(cpuset_migrate_mm_wq); @@ -2039,14 +2046,14 @@ static int cpuset_css_online(struct cgroup_subsys_state *css) /* * If the cpuset being removed has its flag 'sched_load_balance' * enabled, then simulate turning sched_load_balance off, which - * will call rebuild_sched_domains_locked(). + * will call rebuild_sched_domains_cpuslocked(). */ static void cpuset_css_offline(struct cgroup_subsys_state *css) { struct cpuset *cs = css_cs(css); - mutex_lock(&cpuset_mutex); + cpuset_sched_change_begin(); if (is_sched_load_balance(cs)) update_flag(CS_SCHED_LOAD_BALANCE, cs, 0); @@ -2054,7 +2061,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css) cpuset_dec(); clear_bit(CS_ONLINE, &cs->flags); - mutex_unlock(&cpuset_mutex); + cpuset_sched_change_end(); } static void cpuset_css_free(struct cgroup_subsys_state *css) @@ -2275,15 +2282,8 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs) mutex_unlock(&cpuset_mutex); } -static bool force_rebuild; - -void cpuset_force_rebuild(void) -{ - force_rebuild = true; -} - /** - * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset + * cpuset_hotplug - handle CPU/memory hotunplug for a cpuset * * This function is called after either CPU or memory configuration has * changed and updates cpuset accordingly. The top_cpuset is always @@ -2298,7 +2298,7 @@ void cpuset_force_rebuild(void) * Note that CPU offlining during suspend is ignored. We don't modify * cpusets across suspend/resume cycles at all. */ -static void cpuset_hotplug_workfn(struct work_struct *work) +static void cpuset_hotplug(bool use_cpu_hp_lock) { static cpumask_t new_cpus; static nodemask_t new_mems; @@ -2356,25 +2356,31 @@ static void cpuset_hotplug_workfn(struct work_struct *work) } /* rebuild sched domains if cpus_allowed has changed */ - if (cpus_updated || force_rebuild) { - force_rebuild = false; - rebuild_sched_domains(); + if (cpus_updated) { + if (use_cpu_hp_lock) + rebuild_sched_domains(); + else { + /* Acquiring cpu_hotplug_lock is not required. + * When cpuset_hotplug() is called in hotplug path, + * cpu_hotplug_lock is held by the hotplug context + * which is waiting for cpuhp_thread_fun to indicate + * completion of callback. + */ + mutex_lock(&cpuset_mutex); + rebuild_sched_domains_cpuslocked(); + mutex_unlock(&cpuset_mutex); + } } } -void cpuset_update_active_cpus(void) +static void cpuset_hotplug_workfn(struct work_struct *work) { - /* - * We're inside cpu hotplug critical region which usually nests - * inside cgroup synchronization. Bounce actual hotplug processing - * to a work item to avoid reverse locking order. - */ - schedule_work(&cpuset_hotplug_work); + cpuset_hotplug(true); } -void cpuset_wait_for_hotplug(void) +void cpuset_update_active_cpus(void) { - flush_work(&cpuset_hotplug_work); + cpuset_hotplug(false); } /* diff --git a/kernel/power/process.c b/kernel/power/process.c index 50f25cb..28772b405 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -203,8 +203,6 @@ void thaw_processes(void) __usermodehelper_set_disable_depth(UMH_FREEZING); thaw_workqueues(); - cpuset_wait_for_hotplug(); - read_lock(&tasklist_lock); for_each_process_thread(g, p) { /* No other threads should have PF_SUSPEND_TASK set */ diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d17c5da..25b8717 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5590,7 +5590,6 @@ static void cpuset_cpu_active(void) * restore the original sched domains by considering the * cpuset configurations. */ - cpuset_force_rebuild(); } cpuset_update_active_cpus(); } -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.